1. Field of the Invention
The present invention relates to a character display apparatus for an image processing apparatus which is directed to transforming a character signal of a sequential scanning method to a character signal of an interlaced scanning method and displaying the same, and in particular to an improved character display apparatus for an image processing apparatus and a method therefor which are capable of effectively decreasing a flickering phenomenon which occurs due to an interlaced scanning method.
2. Description of the Related Art
FIG. 1 is a block diagram illustrating a conventional image display apparatus. As shown therein, a modem 1 connected to a television receiver demodulates a communication protocol inputted through a network and outputs a character set data, and a video processing unit 3 generates a RGB signal of a sequential scanning method from the character set data using a character font data and a character data which are stored in a ROM 2. At this time, the video processing unit 3 processes the characters at a predetermined speed faster than when it is installed in an internet set top box.
In addition, an NTSC encoder 4 separates the RGB signal of a sequential scanning method from the video processing unit 3 into a chromaticity signal and a luminosity signal and outputs the thusly separated signal to the television monitor 5 for thus displaying a corresponding character on the screen.
The television receiver uses an interlaced scanning method which divides an image of one frame into two fields different from the sequential scanning method which is used for a computer monitor. At this time, each field is separated into an even number field and an odd number field, and the characters are alternately displayed on the even number lines and odd number lines.
Therefore, in the interlaced scanning method, the displayed characters are blinked, namely, a flicker phenomenon occurs. This flicker phenomenon is increased when the character is displayed on only one of either the even number line or the odd number line.
FIG. 2 is a view illustrating a conventional character processing apparatus which is capable of decreasing the above-described flicker phenomenon and includes a character image forming unit 10, a multiple value data transforming unit 11, an edge defocusing unit 12, a signal transforming unit 13 and a character display unit 14.
The operation of the conventional character processing apparatus will now be explained with reference to the accompanying drawing.
First, the character image forming unit 10 forms a binary image within the frame buffer based on a file data or a ROM data using an outline font register. In addition, the multiple value transforming unit 11 transforms the binary font image formed by the image forming unit 10 to a multiple value image including a gray scale by an antialiasing process.
Namely, the pixel which is shown in FIG. 3A is processed to become the pixels of FIG. 3B, and the pixels placed in the upper, lower, left and right sides are given written: 1/2 weights, and the pixels which are diagonally placed are given 1/4 weight for thereby transforming the pixel image to a multiple value font image.
In addition, the edge defocusing unit 12 supplies the multiple value font images outputted from the multiple value data transforming unit 11 with a PSF (Point Spread Function) for thus defocusing the image within the frame buffer.
The multiple value font images which are font-registered as shown in FIG. 4A are filled with the outline vector font. At this time, as shown by "b" of FIG. 4B, angled corner edges are formed. Therefore, as shown in FIG. 4C, the images are sampled four times, and the character fonts are filled. Thereafter, the average values of the pixel density data are obtained, so that the portions which interface with the outline are formed to have an intermediate color tone.
The signal transforming unit 13 transforms the multiple value images placed within the frame buffer to the decoded and interlaced signal or the non-interlaced signal, and the character display unit 14 reproduces the output signal from the signal transforming unit 13 and displays on the monitor.
Therefore, in the conventional character processing apparatus, the images of the characters are defocused by the multiple data transforming unit 11 and the edge defocusing unit 12, so that the difference between the image of the even number field and the image of the odd number field is decreased for thereby decreasing a flicker phenomenon.
However, in the conventional character processing apparatus, it takes significant time for decreasing the flicker phenomenon due to the multiple value transforming process and edge defocusing process, so that a large data processing load is applied to the CPU compared to the OS processing capability of the internet set top box.
In addition, since it is impossible to use a predetermined number of memories in the internet set top box, high speed hardware is required, thus increasing the fabrication cost of the system.